1、 International Telecommunication Union ITU-T P.833.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2009) SERIES P: TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Methods for objective and subjective assessment of speech quality Methodology for the derivation of equipment impairment f
2、actors from subjective listening-only tests for wideband speech codecsRecommendation ITU-T P.833.1 ITU-T P-SERIES RECOMMENDATIONS TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Vocabulary and effects of transmission parameters on customer opinion of transmission quality Series P.10 Voice
3、terminal characteristics Series P.30 P.300 Reference systems Series P.40 Objective measuring apparatus Series P.50 P.500 Objective electro-acoustical measurements Series P.60 Measurements related to speech loudness Series P.70 Methods for objective and subjective assessment of speech quality Series
4、P.80 P.800 Audiovisual quality in multimedia services Series P.900 Transmission performance and QoS aspects of IP end-points Series P.1000 Communications involving vehicles Series P.1100 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T P.833.1 (04/2009) i Recommenda
5、tion ITU-T P.833.1 Methodology for the derivation of equipment impairment factors from subjective listening-only tests for wideband speech codecs Summary Recommendation ITU-T P.833.1 describes an extension of the methodology for deriving equipment impairment factors from subjective listening-only te
6、sts. It is intended that it primarily be applied to determining wideband equipment impairment factors Ie,wb, capturing the degradation introduced by wideband speech codecs. The resulting wideband equipment impairment factors derived by this methodology are intended to be used on the extended transmi
7、ssion rating scale underlying the E-model, see Appendix II of Recommendation ITU-T G.107. They will reflect the auditory impairments of the corresponding equipment in a listening-only mode. Source Recommendation ITU-T P.833.1 was approved on 29 April 2009 by ITU-T Study Group 12 (2009-2012) under Re
8、commendation ITU-T A.8 procedure. Keywords Codec, E-model, impairment factor method, wideband speech transmission. ii Rec. ITU-T P.833.1 (04/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and com
9、munication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
10、The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolutio
11、n 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and
12、a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met.
13、The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibili
14、ty that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recom
15、mendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information
16、 and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T P.833.1 (04/2009) iii CONTENTS Page 1 Sc
17、ope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Selection of experiment parameters 2 6.1 Reference conditions for wideband speech codecs without transmission errors. 3 6.2 Reference conditions for wideband speech codecs with transmission errors. 4 7 Test method
18、 4 8 Derivation of wideband equipment impairment factors . 5 8.1 Scale transformation (step 1) 6 8.2 Linear interpolation of the test results (step 2). 6 8.3 Additivity check (step 3) 7 8.4 Derivation of Ie,wb values for transmission error conditions (step 4) . 7 8.5 Additivity check (step 5) 7 9 Ap
19、plication of the derived wideband equipment impairment factor values. 7 Bibliography. 8 iv Rec. ITU-T P.833.1 (04/2009) Introduction ITU-T has introduced the impairment factor method in order to describe the joint effect of different types of degradations on overall transmission quality. According t
20、o this method, transmission impairments can be transformed into so-called “psychological factors“, which are assumed to be additive on a psychological scale. The transmission rating scale (R-scale) underlying the E-model (see Recommendation ITU-T G.107) is assumed to reflect such a psychological sca
21、le. The impairment factor method allocates a value of impairment to each parameter describing the transmission channel, and then allows the simple addition of these impairments to determine the overall impairment. The overall transmission rating R is finally calculated by subtracting the overall imp
22、airment from the maximum value Rmax. Whereas the R-scale and the E-model have originally been formulated for narrow-band (300-3400 Hz) speech transmission only, Appendix II of Recommendation ITU-T G.107 presents an extension of this scale to wideband (50-7000 Hz) speech transmission. Although a comp
23、lete wideband version of the E-model is not yet available, Appendix IV of Recommendation ITU-T G.113 provides values for wideband equipment impairment factors Ie,wb, which describe the degradation resulting from selected wideband speech codecs on the extended R-scale. This Recommendation describes a
24、 methodology for how Ie,wb values can de derived for other wideband speech codecs, from the results of listening-only tests. Rec. ITU-T P.833.1 (04/2009) 1 Recommendation ITU-T P.833.1 Methodology for the derivation of equipment impairment factors from subjective listening-only tests for wideband sp
25、eech codecs 1 Scope It is assumed that users of this Recommendation are familiar with ITU-T P.833. The extension of the methodology described in this Recommendation is intended to derive wideband equipment impairment factors Ie,wb quantifying the impairment introduced by wideband (50-7000 Hz) speech
26、 codecs, including or not the effects of transmission errors, such as random bit errors, random packet loss or discard, or bursty packet loss or discard. Such wideband equipment impairment factors have been introduced as a simplified measure of the degradation introduced by wideband speech codecs on
27、 the integral transmission quality from mouth to ear. They are in no way an exact description of the effects related to each individual codec or codec tandem, which may be very diverse in their perceptual nature. Instead, they represent the relative degradation in comparison to other impairments occ
28、urring in a connection. In order to provide guidance on the quantitative amount of impairment introduced by such codecs, a framework of wideband equipment impairment factor values for several wideband speech codecs has been derived by ITU-T, see Appendix IV of ITU-T G.113. The derivation of these va
29、lues was based on many subjective listening-only tests carried out in different test laboratories, so as to guarantee stable values for all the codecs under investigation so far, as well as their relations to each other. If new equipment impairment factor values for different codecs have to be deriv
30、ed, then the overall consistency with the established framework is of primary importance if results are to be obtained that are valid for network planning. The methodology described in this Recommendation was designed to fulfil this requirement. So far, wideband speech codecs are the only wideband e
31、lements for which impairment factors have been derived. For asynchronous tandems of multiple codecs of the same type, or of multiple codecs of different types, it is assumed that individual equipment impairment factors are additive. The overall equipment impairment factor for the chain of codecs is
32、then calculated as a simple sum of all the individual Ie,wbs. Experimental test data collected provide evidence that this simple additivity is not satisfied for all the potential combinations of codecs b-Mller. In some cases, order effects exist, i.e., the tandem of codec A followed by codec B resul
33、ts in a different degradation than codec B followed by codec A. These deviations from the pure additivity property are an item for further study. Impairment factor values for other wideband network elements, resulting in other types of degradations and to be used in a wideband version of the E-model
34、, have not yet been defined and are for further study as well. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid.
35、All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is
36、regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.107 Recommendation ITU-T G.107 (2008), The E-model, a computational model for use in transmission planning. 2 Rec. ITU-T P.833.1 (04/2009)
37、ITU-T G.113 Recommendation ITU-T G.113 (2007), Transmission impairments due to speech processing. ITU-T G.722 Recommendation ITU-T G.722 (1988), 7 kHz audio-coding within 64 kbit/s. ITU-T G.722.1 Recommendation ITU-T G.722.1 (2005), Low-complexity coding at 24 and 32 kbit/s for hands-free operation
38、in systems with low frame loss. ITU-T G.722.2 Recommendation ITU-T G.722.2 (2003), Wideband coding of speech at around 16 kbit/s using Adaptive Multi-Rate Wideband (AMR-WB). ITU-T P.341 Recommendation ITU-T P.341 (2005), Transmission characteristics for wideband (150-7000 Hz) digital hands-free tele
39、phony terminals. ITU-T P.800 Recommendation ITU-T P.800 (1996), Methods for subjective determination of transmission quality. ITU-T P.830 Recommendation ITU-T P.830 (1996), Subjective performance assessment of telephone-band and wideband digital codecs. ITU-T P.833 Recommendation ITU-T P.833 (2001),
40、 Methodology for derivation of equipment impairment factors from subjective listening-only tests. 3 Definitions None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ADPCM Adaptive Differential Pulse Code Modulation CELP Code Excited Linear Prediction
41、MLTC Modified Lapped Transform Coding MOS Mean Opinion Score 5 Conventions None. 6 Selection of experiment parameters The listening-only test from which Ie,wb values are to be derived should fulfil the general requirements for listening-only tests given in ITU-T P.800 and ITU-T P.830, as well as the
42、 requirements set in ITU-T P.833. However, in contrast to ITU-T P.833, the test should be carried out in a wideband or mixed-band mode, implying several changes given hereafter. In contrast to narrow-band, there is no standard wideband terminal which would be representative for most wideband connect
43、ions. For the given purpose, the test should be carried out either with diotic or monotic headphone presentation. The frequency response of the terminal should represent a wideband characteristic in the range 50 to 7000 Hz, as it is defined in ITU-T P.341. For reasons given in ITU-T P.833, subjectiv
44、e tests aiming at deriving equipment impairment factors should include a number of reference conditions. These references are necessary for anchoring impairment factor values, and they will guarantee that new equipment impairment factor values fit into the existing system given in Appendix IV of ITU
45、-T G.113. Rec. ITU-T P.833.1 (04/2009) 3 It is recommended that different types of wideband speech codecs be used as a reference for experiments deriving wideband equipment impairment factors (i.e., waveform codec as G.722 or hybrid codec as G.722.2). The exact reference conditions to be used vary d
46、epending on whether transmission errors are to be considered, and whether an additivity check has to be performed. In addition, a narrow-band codec may be used in case of mixed-band test. 6.1 Reference conditions for wideband speech codecs without transmission errors When wideband equipment impairme
47、nt factors for codecs disregarding transmission errors are determined, the set of 12 reference codec conditions given in Table 1 should be included in the subjective test conditions. This list has been chosen from the codecs for which values are already defined in Appendix IV to ITU-T G.113, and the
48、y have been selected to cover the whole range of Ie,wb values. Table 1 Reference conditions for wideband speech codecs without transmission errors No. Abbreviation Codec type Reference Operating rate (kbit/s) Ie,wb value 1 Clean Linear PCM, 16 bit 0 2 G.722.223.05 CELP ITU-T G.722.2 23.05 1 3 G.722.
49、219.85 CELP ITU-T G.722.2 19.85 3 4 G.722.215.85 CELP ITU-T G.722.2 15.85 7 5 G.722.214.25 CELP ITU-T G.722.2 14.25 10 6 G.72264 ADPCM ITU-T G.722 64 13 7 G.722.132 MLTC ITU-T G.722.1 32 13 8 G.722.124 MLTC ITU-T G.722.1 24 19 9 G.72256 ADPCM ITU-T G.722 56 20 10 G.722.28.85 CELP ITU-T G.722.2 8.85 26 11 G.72248 ADPCM ITU-T G.722 48 31 12 G.722.26.6 CELP ITU-T G.722.2 6.6 41 It is important to check the additivity of the newly derived wideband equipment impairment factor in the framework of other equipment impairment factor values d
